Attenuators



Oct. 22, 1957 H. F. ENGELMANN ATTENUATORS Filed March 3, 1954 INVENTOR #m35/er E NGfL/WANN lll'lllllll'nll ATTORNEY United States 2,810,891 ATTENUATORS Herbert F. Engelmann, Mountain Lakes, N. J., assigner to International Telephone and Telegraph Corporation, Nutley, N. J., a corporation of Maryland Application March 3, 1954, Serial No. 413,805 3 Claims. (Cl. S33-81) This invention relates to radio frequency attenuators and more particularly to an attenuator adapted for use in connection with the Microstrip type of waveguide.

It has recently been discovered that a simple lineabove-ground type of transmission line may be employed for propagation of high and ultra high radio frequency energy. This type of transmission line, which is disclosed in my Patent No. 2,654,842, is known as Microstrip. More particularly, the Microstrip waveguide comprises a pair of conductors, one wider that the other, dielectrically spaced apart in parallel relation. The two conductors may be applied to a layer of dielectric material by known printed circuit techniques, one being in the form of a planar conductor and the other a narrow striplike line conductor. The propagation of radio frequency energy is in a manner similar to the TEM mode in that the distribution of the electric field is substantially the same as that which occurs between one conductor and the neutral plane of a truly parallel two-wire transmission line.

Certain types of attenuators, both fixed and pivoted, are disclosed in the joint application of D. D. Grieg, H. F. Engelmann and J. A. Kostriza, Serial No. 229,172, tiled May 3l, 1951, now Patent No. 2,725,535. While these disclosures are effective as attenuators for the Microstrip type of line, I have found that it is essential to provide resilient engagement between the attenuator pad and the strip conductor to ensure more satisfactory control of the amount of attenuation desired. It is one of the objects of the present invention, therefore, to provide a relatively simple, easily constructed attenuator which provides for resilient engagement of the attenuating pad with respect to one of the conductors of the Microstrip type of waveguide. Another object of the invention is to provide forms of attenuators which provide for easy adjustment of the amount of attenuation desired and yet maintain the attenuator pad thereof in a desired resilient engagement with respect to one of the conductors of the Microstrip waveguide.

One of the features of the invention is the provision of an attenuator pad which is disposed for pivotal movement relative to the strip conductor wherein the pivoted connection is biased resiliently toward the planar conductor and in overlapping engagement with the strip conductor. In addition to the biased arrangement, a resilient dielectric plate is disposed in overlying relationship with respect to the strip conductor in such spaced relation as to receive the pad between the plate and the strip to ensure satisfactory engagement between the pad and the strip for the entire area of overlap. The plate is also provided with means for determining the position of the pad for predetermined areas of overlap with respect to the strip conductor.

A further object is to provide an attenuator pad arrangement which is particularly suitable for experimental work with Microstrip components. In this form, the attenuator pad is urged in overlapping relation to the strip conductor by means of pins supported in a bracket adapted to straddle the strip conductor. The pins are provided with springs to resiliently urge the ends of the pins in engagement with the pad.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is a view in plan of one embodiment of the invention;

Fig. 2 is a ycross-sectional View taken along line of Fig. 1; and

Fig. 3 is a view in perspective with parts broken away and in section to show a further embodiment of the invention.

Referring to Figs. l and 2, the attenuator therein shown comprises a section of Microstrip waveguide which includes a first or planar conductor 1, a second or strip conductor 2 and a layer of dielectric material 3 which separates the conductors 1 and 2 in parallel relation. The dielectric material may comprise polyethylene, polystyrene, Teflon (polytetraiiuoroethylene), fiber glass or lamination of ber glass and Teflon, or other suitable material of dielectric quality, or if Microstrip structure permits the dielectric may even be air. The conductor 1 and dielectric layer 3 are provided with an opening 4 through which a pin 5 is disposed. The planar conductor 1 is provided with a sleeve 6 which surrounds the pin extending therethrough. The lower end of the pin 5 is threaded to receive a nut 7, the upper end of which is adapted to be received in the sleeve 6. Disposed in coaxial relation about the pin 5 is a spring 8 which engages the nut 7 at one end and the conductor 1, or the dielectric layer 3 as may be desired at the other end to exert a resilient downward pull on the pin 5. An attenuator pad 9 of lossy dissipative material, such as mixtures of dielectric, conductive and/ or resistive substances of the iron group, is pivotally carried by the pin 5 for movement to positions overlying the strip conductor 2. The pad may be of any particular shape desired, one shape being curved as illustrated at itl so that the degree of area overlap with respect to the strip conductor 2 may be varied while at the same time presenting a small acute angle in the direction of the strip.

While the spring 8 provides for a resilient force to effect positiveengagement between the pad 9 and the strip 2, I also provide a plate of dielectric material 11, which is carried by the layer 3 in spaced overlying relationship with respect to the strip 2. The spacing of the plate 11 with respect to the strip 2 is selected slightly less than the thickness of the pad 9 so as to ensure positive resilient bias against the upper surface of the pad as it is moved into overlying engagement with the strip 2. The pad 11 is preferably slightly turned upwardly along its free edge 12 as indicated so as to readily receive the pad as it is moved into overlying engagement with the strip 2. The plate 11 is preferably secured by means of rivets or eyelets 13 extending through the dielectric layer 3 and planar conductor 1. To determine definitely certain overlying positions of the pad 9, a series of openings 1d are provided in the plate 11 to receive a key 15 against which the edge of the pad 9 is adapted to abut thereby limiting its position.

From the foregoing description of Figs. 1 and 2, it is clear that this embodiment provides an attenuator for Microstrip waveguides which may be applied to the Microstrip circuitry either as an addition to such type of waveguide or it may constitute a section of Microstrip waveguide incorporating the pads substantially as shown. The curvature of the pad provides for ne adjustment of the attenuation and the resiliency of the plate 11 with or without the presence of the spring 8 ensures satisfactory resilient engagement of the pad withrcspect to the strip conductor.

In Fig. 3, the attenuator includes a bracket 16 in the form .of a channel member adapted to straddle Va strip jconductor 2a. Thisnformv is particularly useful` inexper'mental work'where it is desirable to apply an attenuator pad over different parts of Microstrip circuitryfor experimental purposes.V The bracket is of suifcient Weight to provide in conjunction with pinsrl? and 1S theldesired pressure against the pad 19 disposed in overlying engagement with the strip 2a. The pins 17 and 1S are disposed throughY openings contained inthe bracket 16, the lower end of each pin having an enlarged portion 20 adapted to engage theV pad 19. Each pin is provided with a spring ZI disposed in coaxial relation thereabout, one end being YinV engagement with the enlarged portion 20'while the other endV engages e bracket 16 `to ensure thel desired resilient pressure against the pad 19.

While I have described above the principles of my,

invention in connection with specilic apparatus, it is to be clearly understood that this description is made only by way of example` and not as a limitation to the scope of I claim: Y y y 1. An attenuator Vfor high frequency waves comprising rst and second conductors, a layer of dielectric material Vmy invention, as set forth in the objects thereof and in the accompanying claims.

interposed between said conductors to maintain them in Y electric iield distribution betweenone conductor and the neutral planeof a truly parallel two-conductor line, a pad of dissipative material, means supporting said pad for adjustableV movement' crosswise of said second 'conductor and-a plate of dielectric material disposed' n overlying spaced relation to said second conductor over which said pad is movable, the spacing between said plate and said second conductor being normally less than the thickness fof-said pad sothat'when said pad is moved between said plate and said second conductor said plate resiliently urges said pa'd against said secondV conductor.

2. An attenuator for high frequency waves comprising first and secondy conductors, a layer of dielectric material interposed between said conductors to maintain them j' in close, dielectrically spaced parallel relation, said second conductor being ribbon-like in configuration and said first conductor being wider than said second conductor to present thereto a planar surface whereby the electric field distribution of highv frequency waves propagated Y 4v along said conductors is substantially the same as the electric eld distribution between one conductor and the neutral plane of a truly parallel two-conductor line, a pad of dissipative material, a plate of dielectric material disposed in overlying spaced relation to said second conductor wherein said spacing is normally less than theV 3. Anattenuator for high frequency y.waves comprising t iirst and second conductors, a layerof dielectric material interposed between said conductors to maintain them in i close, dielectrically spaced parallel relation, said second conductor being ribbon-like in configuration and said first conductor being wider than said second conductor to present thereto a planar surface whereby the electric field distribution of high lfrequency Waves propagatedV along said conductors is substantially the same as the electric field distribution between one conductor and the neutral plane of a truly parallel two-conductor line', a pin disposed through said layer or" dielectric and through said first conductor, a pad of dissipative material disposed on said pin, a spring disposed coaxially on said pin on the underside of said first conductor, a nut receivable on said pin where-V by the tension of the spring between said nut and sad first conductor may be determined by the position of saidV nut on said pin toV thereby resiliently urge said pad in overlying engagement with said second conductor,-a plate of dielectric material disposed in overlying space'd relation to said second conductor wherein said spacing is normally less than the thickness of said pad so that when said pad is moved between said plate and said second conductor said plate resiliently urges said pad in conjunction with said spring against said second con- Y ductor, said plate having a series of openings and a key for selective positioningtrin'said openings to limit the position of said pad withV respect to the area or' overlapy with respect to said second conductor.

References tCited Vinthe iile of thispatentrV OTHER REFERENCES Proceedings of the I. R. E.; vol. 40, December 1952; pages 1644-1650; 333-84M- Serial No. 694,044, Bollinger et v a1. (A. P. C. published November 21, 1950, O. G. 1032. Y 

